They will need to sooner or later. Linux has more momentum than ever, and saying "players on steam deck/steam machine/bazzite can't play our game" seems like a losing long term strategy.
I can't say which has more weight but it's not a cut and dry situation, at least until Linux has anti-cheat.
Right now developers could make an "unattested" queue for linux and other non-TPM windows systems. Which could also serve as a black-hole for cheaters, so maybe there's some value in that.
I predict they won't allow all Linux but only the specific version Valve puts on the Steam Deck/Machine, and if you modify it then your games won't run again.
>It's supposed to be modifiable.
https://www.kernel.org/linux.html
I have not seen that as a project goal.